The vast majority of Citi Bike riders are men, a new study from NYU's Rudin Center for Transportation says, with most trips originating from heavily-trafficked areas like Midtown. Women comprise only 23.7 percent of subscription-based riders, and generally prefer to stick to the comparatively bucolic streets of brownstone Brooklyn.

Why is that? The predominant reason is safety, the study says. Women tend to choose stations "with fewer lanes of traffic, more limited truck traffic, fewer collision-based cyclist injuries in recent memory, and in some cases, fast access to bridge entrances; men most often chose stations with more traffic, some truck traffic, some collision-based cyclist injuries, and, typically, connectivity to major transit hubs."

This is consistent with female ridership numbers in general—a study by Hunter College released in February found that 78 percent of the city's cyclists are men. While the disparity is certainly enormous, it used to be bigger—in 2009, 91 percent of riders were men. Women also tend to be safer riders, the study found, and more inclined to obey traffic signals and wear helmets.

Thus, the key to encouraging more women to ride is simple: Make the streets safer. Women, with their apparent abundance of caution, act as a barometer for the overall safety (or perceived safety) of a given street: The most popular station for women is located in the East Village, at 8th Street and Avenue D. Though it lacks a dedicated bike lane, it does have limited transit access, relatively mellow traffic and easy access to the East River waterfront and bridges—all excellent uses for Citi Bikes or bicycles in general. By continuing to strengthen cycling infrastructure, it's certain that more women will feel comfortable turning to riding as a transit option.

We'll know the streets have reached Peak Safety the day we see a woman carrying a baby on her handlebars. Our research shows it will be awhile.